built across the creek in 1960. Additionally, two bridges carrying Interstate 80 were built over the creek in 1962 and repaired in the late 1990s. A bridge carrying State Route 4004 over the creek was built in 1987 and another bridge carrying Pennsylvania Route 54 was built in 1992. A bridge carrying State Route 1003 was constructed across the creek in 1993 and a bridge carrying State Route 3003 was built over the creek in 1997. In 2005, another bridge carrying State Route 1004 was built over the creek. A number of bridges have been built over Chillisquaque Creek in Northumberland County as well. One of these was the Rishel Covered Bridge, which was built in 1830 and repaired in 1990. It is listed on the National Register of Historic Places. The Gottlieb Brown Covered Bridge, which carries T594, was built across the creek in 1881 and was repaired in 1985. It is also on the National Register of Historic Places. A bridge carrying State Route 1025 was constructed over the creek in 1926 and a bridge carrying Pennsylvania Route 45 was built over the creek in 1952. A three-span bridge carrying Pennsylvania Route 642 was built over the creek in 1958 and was repaired in 2012. A two-span bridge carrying Pennsylvania Route 405 was built over the creek in 1974. A number of studies and inventories have been carried out on Chillisquaque Creek. Such studies include Pennsylvania's 208 Study in 1979, an assessment by the Pennsylvania Department of Environmental Protection, and an assessment by Bucknell University in 2003. Biology The drainage basin of Chillisquaque Creek is designated as a Warmwater Fishery and a Migratory Fishery. The creek was observed by A. Joseph Armstrong to lack trout. In 1986, the creek was not being stocked. However, it was stocked with black bass, sunfish, and yellow perch in 1934 and with yellow perch in the spring of 1936. In 1986, it contained many of the species found in the West Branch Susquehanna River, including rock bass. Smallmouth bass have also been observed in the creek. Disease is moderately common among young-of-the-year smallmouth bass in the creek. 2011 was the first year where diseased smallmouth bass were documented in the creek since studies began in 2009. A tract of forested floodplain known as the Chillisquaque Creek Natural Area (or Bucknell Preserve, Tobias Marsh, or Mexico Road Swamp) is located in Liberty Township,